The present invention relates to radio frequency antennas employing reflectors. In particular, the present invention relates to a deployable reflector for an electronically scanned antenna system.
Antennas are used to radiate or receive radio wave signals. The transmission and reception of radio wave signals is useful in a broad range of activities. For instance, radio wave communication systems are desirable where communications are transmitted over large distances.
One type of antenna for use with radio wave communications is the reflector antenna. Reflector antennas typically feature a relatively large reflector surface, to increase the gain of the antenna. The reflector surface may take any one of a number of geometrical configurations, such as plane, corner, and curved configurations
An electronically scanned reflector antenna is an antenna that uses a phased array feed to illuminate a nearby reflector unit in order to generate one or more steerable antenna beams. Such antennas are increasingly used in space-based applications such as, for example, satellite communications applications. As can be appreciated, it is difficult to transport large antenna reflectors into space. Therefore, it is desirable to have a deployable reflector that can be collapsed into a relatively small volume for transport, and deployed as a relatively large reflector surface at the antenna site.
It is desirable that a reflector for an antenna be relatively inexpensive to construct. In addition, it is desirable that such a reflector have a precisely controlled surface geometry to ensure the highest possible antenna efficiency. Previously, deployable antennas using fabric-type reflector surfaces have been constructed from single pieces of fabric or several large pieces. Such reflector assemblies are expensive and difficult to manufacture, as it is difficult to control the shape of large pieces of fabric, particularly where the reflector has a curved surface. Other fabric-type reflectors have used relatively small, complex pieces of fabric that are joined to one another, again resulting in a reflector that is difficult and expensive to manufacture. Still other fabric type reflectors use an xe2x80x9cumbrellaxe2x80x9d type deployment mechanism having the shape of a paraboloid, with ribs that are bowed, and therefore shaped, by the fabric of the reflector surface. In addition, previous fabric-type antenna reflector designs have been incapable of providing a large reflector surface having a precisely controlled surface geometry to provide high gain, a small storage volume, and a reliable deployment mechanism in a space-based antenna application.
Therefore, there is a need for a method and apparatus for providing a large reflector surface for space-based antenna applications. In particular, there is a need for a method and apparatus for providing such a reflector that can be stowed in a relatively small volume for transportation to the antenna site, and deployed at the site automatically to provide a reflector surface having high gain. Furthermore, there is a need for a large reflector surface suitable for use in connection with an electronically scanned reflector antenna system. In addition, such a method and apparatus should be relatively easy to manufacture and operate.
In accordance with the present invention, a deployable antenna reflector for a space-based antenna system is disclosed. The reflector generally includes a plurality of fabric panel members and a connecting assembly interconnected to the panel members, and movable from a stowed state into a deployed state. In a stowed state, the components of the connecting assembly are within a relatively small distance of one another, and the fabric of the plurality of panel members is folded. In a deployed stated, the components of the connecting assembly are moved apart from one another to hold the panel members in tension, thereby forming a reflector surface.
The panel members generally comprise identical panels of fabric or metallized flexible dielectric sheets, each having associated attachment members. The attachment members provide a convenient means for attaching the panel members to the connecting assembly. In addition, the provision of the panel members in one or a small number of sizes facilitates assembly of the reflector, and reduces the cost of the reflector.
The connecting assembly generally includes ribs having contoured front surfaces for shaping the panel members and thus the reflector when the reflector is in a deployed state. The ribs are generally carried by an extendable boom.
When the reflector is in a stowed state, the ribs are in relatively close proximity to one another. According to one embodiment of the present invention, each rib can also be folded about a centrally located hinge, so that the reflector can be placed in a relatively small container for transportation. Upon deployment, the ribs are opened about the centrally located hinges, and the boom is extended, moving the interconnected ribs apart from one another. The extension of the boom additionally tensions the panel members, which are held between adjacent ribs, forming the reflector surface. According to one embodiment of the present invention, adjacent panel members in a row are affixed to the same pair of ribs, but are not directly interconnected to one another.
For use as part of an antenna system that will be located in a remote location such as the polar regions of Earth or in space, the reflector assembly is placed in a first, or folded, condition, and is transported to the antenna site. Once at the antenna site, the reflector assembly is placed in a second, deployed state in which the plurality of panels is held in tension between individual ribs of the connection assembly to form a reflector surface.
The present invention includes a method of forming panel members for use in a deployable antenna reflector. According to this method, a foldable fabric having a surface capable of reflecting electromagnetic radiation is formed into regularly sized panels. The panels are affixed at a first end to a first attachment member, and at a second end to a second attachment member. The panels are next placed under a predetermined amount of tension, and holes are formed through the first and second ends of the panel. The panel is then ready for use in a reflector assembly.
Based on the foregoing summary, a number of salient features of the present invention are readily discerned. An antenna reflector having a large surface area when deployed, but requiring a small volume for transport, can be provided. The antenna reflector provides a high gain, due to its large size and precise surface control. The antenna reflector is well suited for use in space-based applications, as it can be compactly stowed for transportation to the antenna site, and deployed at the site without direct human intervention. The antenna reflector can be formed from a plurality of like-sized panels to increase the accuracy of the reflector surface when deployed, and to decrease manufacturing costs.
Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings.